The Building Conservation Directory 2023

I N T E R I O R S 5 159 C AT H E D R A L C O M M U N I C AT I O N S T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 2 3 | C E L E B R AT I N G 3 0 Y E A R S ENCAUSTIC TILES The inspiration for encaustic tiles came from the discovery of medieval tiles with an inlay of a lighter colour, forming a simple motif such as a rose or a lion. In 1830, Samuel Wright of Shelton, Stoke- on-Trent took out a patent for the process of manufacturing a tile with an indented pattern pressed into it. The indent would then be filled with a relatively fluid clay of a contrasting colour. When dry the surface would be cut back to reveal the clean edges of the pattern and then fired. After initial teething problems with varying shrinkage rates, the process was refined by another ceramics manufacturer in Stoke, Herbert Minton. The first successful application was in 1841 when Minton made replicas of medieval tiles found in Westminster Abbey. Their installation in Temple Church, London accorded well with the expanding Gothic Revival, and two years later Minton’s encaustic tiles were used by its leading advocate, AWN Pugin for his own home, The Grange. Pugin was one of a growing movement whose members considered classical architecture to be pagan, while gothic was Christian, and therefore the only fitting style for a Christian country. His arguments were persuasive and he worked closely with Herbert Minton on the development of new tiles that adapted the medieval designs for the Victorian age. Those they produced for the new Houses of Parliament between 1847 and 1852 were far more elaborate than their medieval counterparts, introducing a bright blue inlay to add a splash of colour. When Wright’s patent ran out in 1850 many other manufacturers began making encaustic tiles, and their costs fell further following the introduction of dust-pressing by William Godwin around 1870. This involved compressing powdered clay with a very low moisture content between two halves of a mould at high pressure. The low moisture content meant that far less time was needed to dry the tiles and there was less chance of the tiles distorting during drying or firing. GLAZED TILES In the 17th and much of the 18th centuries, decorative tiles in Britain followed the style of Delft in the Netherlands. Delft tiles had simple patterns painted in blue on a white background, and are most often found around fireplaces. Like most glazed ceramics, these tiles were fired twice, once unglazed (the ‘biscuit’ firing) and then after glazing. The natural colour of the clay used to make these tiles was hidden beneath a tin glaze, an opaque white coating which was applied to the surface of the unglazed fired clay. Once dry, the decoration was carefully applied so as not to smudge the unfired tin glaze. To ensure a regular pattern was followed, the pattern had to be dusted or ‘pounced’ onto the surface through a stencil which left little dots for the craftsperson to follow. The design was then painted in using cobalt oxide. In the second firing the particles of the glaze fuse together to form a glossy white ground, while the cobalt turns blue by reduction in the kiln. This laborious process of decoration was eventually avoided following the development of transfer printing in the second half of the 18th century. Scenes and patterns could now be printed from an engraved copper plate onto sheets of specially prepared paper (gelatine was used instead of paper initially) and then transferred to the tin glazed tile. Not only was this a much faster process, but it also allowed for far more detail to be transferred to the piece accurately, without distortion, transforming the medium. By the end of the century the development of pale, almost white clay bodies by companies like Wedgewood allowed the transfer decoration to be applied directly to the body of the clay and then overlayed with a clear glaze. This protected the decoration from wear, and both the decoration and the glaze could be fired at the same time. The clear glaze also added a glossy finish to the tile. A slight variation in thermal contraction rate between the glaze and the clay body could lead to ‘crizzling’, a pattern of fine cracks in the glaze surface, either immediately as it cooled, or decades later. Surface-decorated tiles benefited from the development of dust-pressing long before encaustic tiles did. The first patent was taken out by Richard Prosser in 1840 for making ceramic buttons, and it was almost immediately taken up by Minton for the production of flat tiles. After pressing, the tiles were biscuit fired and then decorated, glazed and fired again. Dust-pressing also enabled clay tiles to be decorated with a raised pattern by pressing an incised die into the clay. When this relief ornament was given a coloured translucent glaze, rich variations in colour Detail of salvaged medieval tiles at Gloucester Cathedral: Herbert Minton realised that by stamping a design into soft clay of one colour and then infilling with clay of a different colour, these inlaid tiles could be mass produced. could be created as the glaze lay thinly over the raised areas, while the recesses where it pooled were much darker. This technique was used to great effect on the wall tiles in Coleridge Chambers (overleaf), most obviously on the dado rail and the four- leafed tiles. A tile being made in a frame: a simple stamp is applied to the reverse to show who made it. (Photo: Craven Dunnill Jackfield) Making an encaustic tile for the Palace of Westminster: the mould is in the craftsman’s hands and the newly pressed tile is on the bench; when fully dried the indented pattern will be infilled with a fluid slip. (Photo: Craven Dunnill Jackfield)